This invention relates to the field of assembled tubing and fittings, for assembly of sub components comprising metal tubing sections.
Metal tubing is assembled into a component by means of standardized metal threaded fittings which serve to provide a positive mechanical interconnection between tubing sections and which also must serve to seal the tubing to prevent leaks when fastened. Fittings are often brazed to the tubing to provide such a seal.
It is desirable to provide a unitary mechanical assembly of preformed tubing sections with installed fittings. To insure proper assembly and seal of fitting to tubing end, the fitting is assembled onto the tube end and brazed to the tubing. Uneven expansion rates encountered in the brazing process can cause separation forces between tubing end and fitting, breaching the brazed seal. Additionally, during the brazing step the brazing material or solder is free flowing, and the flow of this brazing material must be controlled to prevent loss of seal or contamination of fitting surfaces by brazing material.
U.S. Pat. No. 4,887,853 discloses a fitting and process for mechanical assembly of the fitting to a tubing end prior to brazing. However the disclosed fitting requires the machining of an internal undercut counter bore within the fitting as well as the use of a stepped mandrel to expand the tubing end into the counter bore. The resulting assembly is difficult to inspect for complete sealing, and is not designed to prevent flow of brazing metal into the interior bore of the fitting.